1. Field of the Invention
This invention relates generally to atomic particle physics and specifically to a process and apparatus for the preparation of a stable antimatter element, and to the element itself. In particular, this invention relates to a process and apparatus for the preparation of antihydrogen.
2. Brief Description of the Prior Art
Antihydrogen is the simplest of the antimatter elements. It consists of a nucleus including a single antiproton nucleus enveloped by a single orbital positron. In contrast to exotic atomic species such as positronium and muonium, in the absence of reaction with normal matter, antihydrogen is a stable species having an indefinite half life.
It has been previously proposed that antihydrogen be formed at high laboratory energies by reaction of antiprotons and positrons at low relative center of mass energies, in analogy to the reaction of protons and electrons to form hydrogen. However, previously proposed processes are not expected to easily produce antihydrogen in sufficient densities that can be detected to permit measurement of its physical and chemical characteristics, or use as a probe in the analysis of the properties of other materials.
For example, it has been noted that the recombination of two charged particles, such as an antiproton and a positron, requires either a coupling to an electromagnetic radiation field, or the presence of a third massive particle to which energy and momentum can be transferred. However, at present anti-particle beams are only available at such low densities that the probability of antihydrogen formation through three-body interactions is negligible.
Alternatively, antihydrogen may be produced by recombination of antiprotons and positrons with simultaneous radiative emission. The cross-section for spontaneous radiative recapture can be enhanced by stimulating the emission, thus the use of a laser to stimulate recombination in overlapping beams of antiprotons and positrons has been proposed. However, under the proposed experimental conditions no more than 0.004 antihydrogen atoms per second are expected to be produced and at very high velocities. This makes detection of the antihydrogen problematic.
A number of measures have been proposed to increase the antihydrogen formation rate. For example it has been suggested that the positron beam be bunched and the phase of the beam be matched with applied laser pulses to maximize stimulated radiative recombination. Other measures proposed include increasing the positron beam intensity by recirculation of the positrons and improved positron moderation techniques.
An alternative to the cross-beam experiment is storing positrons and antiprotons simultaneously in an ion trap such as a quadrupole trap operated with an RF potential, and inducing reaction within the trap. At cryogenic temperatures (around 1.degree. Kelvin) the spontaneous radiative recombination rate is high. On the other hand, at these low temperatures space-charge effects limit the stored particle density and consequently appear to limit the antihydrogen formation rate to about 10 per second. The particle trap makes antihydrogen atoms available at relatively low kinetic energies in the laboratory frame so that experiments relating to precise measurements of antihydrogen properties can be easily performed. But antihydrogen is expected to leave the quadrupole trap in arbitrary directions, unless the temperature can be reduced sufficiently so that the antihydrogen atoms can be trapped in magnetic field gradients acting on the positron magnetic moment. In contrast, the overlapping beam experiment is expected to produce a well-directed highly collimated antihydrogen atom beam. However, the antihydrogen atoms of the beam would have relatively high kinetic energy making precise measurements of the atomic properties of antihydrogen difficult.
Antihydrogen, the simplest antimatter element, is an extremely potent energy storage medium. Presently, the collision of antimatter particles with their corresponding normal matter particles (antiproton-proton) in cross-beam accelerators yield the highest levels of interaction energy obtainable (around 1.8 trillion electron volts, Tevatron accelerator, Fermi National Accelerator Laboratory). The interaction of hydrogen and antihydrogen is an important annihilation reaction of matter and antimatter at temperatures below 10.sup.5.degree. Kelvin.
Once the physical properties of antihydrogen itself have been measured and compared with those predicted by theory, it can be expected that antihydrogen will find significant use as a probe in the analysis of the properties of normal matter.
There is a need for a process for producing antihydrogen in detectable quantities at low energies, to permit study of the fundamental physical properties of antihydrogen itself, and to provide the antihydrogen as an analytical probe for the study of the properties of normal matter and for use as an energy storage medium.